Solutions of water-insoluble metaphosphates



Patented Jan. 21, 1947 UNITED STATE SOLUTIONS OF wA'rEE-IN's'oLUBLEMETAPIIOSPHATES Henry A. Jackson, Mount Lebanon, Pa-., assignor Y toHall Laboratories, Inc.,

corporation of Pennsylvania Pittsburgh, Pa., a

No Drawing. Application April'Z, 1941, l I: Serial No. 386,501 f' 6Claims. (01. 106-48) This invention relates to aqueous solutions ofwater-insoluble metaphosphate, and more particularly to highly viscousaqueous solutions of such-metaphosphates, the viscous solutions beingsuitable as vehicles forceramic pigments for forming a vitreous orceramic paint or enamel.

. -The present application is a continuation-121+ part of myapplication, Serial No. 143,129, filed May .17, 1937.

The viscosity of these highly viscous, aqueous solutions is unusuallygreat, surpassingthe viscosity of solutions of almost all otherinorganic materials and approaching in viscosity materials such as glue,bentonite suspensions and the like.

I have found that ceramic pigments may be mixed with a viscous aqueoussolution of metaphosphates to form a paint or enamel which is suitablefor decorating ceramics or glassware. After the paint is applied, theceramic article may be burned, to vitrefy it, leaving a hardened film onthe article. The vitreous metaphosphate paint may be used in place ofceramic paints now known which consist of a pigment and an oil as avehicle, My paint has the advantage that upon burning the article, ahard vitreous film is formed which has good adherence to the article.

The metaphosphate which I prefer to use in forming the viscous aqueoussolution which may be employed as a vehicle for ceramic pigments iscrystalline potassium metaphosphate (KPOs). Crystalline potassiummetaphosphate is substantially water-insoluble, so that it is notsuitable when used for forming aqueous solutions. Crystalline potassiummetaphosphates may be made by the dehydration of monopotassiumorthophosphate at elevated temperature, for example at a red heat. Itmay be made at a temperature as low as 300 C. by heating until no morewater is evolved, or it may be made by heating to above the meltingpoint of potassium metaphosphate, which is approximately 810 C., andallowing the melt to cool. The solubility of crystalline potassiummetaphosphate is approximately 40 P. P. M. in distilled water (Potassiummetaphosphate: a potential high-analysis fertilizer material, by S. L.Madorsky and K. G. Clark, in

"Industrial and Engineering Chemistry, vol. 32,

pages 244-8 [1940]). As contrasted with this. the solubility of glassysodium metaphosphate commonly known as Grahams salt is almost unlimited.Solutions containing as much as 30 or 40% by weight can readily beprepared in a short period of time. Therefore, by comparison crystallinepotassium metaphosphate is substantlally 2 r t water-insoluble and wehave thus characterized it in this application. I l

I have found, however, that a viscous aqueous solution of thewater-insoluble crystalline potassium metaphosphate may be made bydissolving the potassium metaphosphate in an aqueous solution containingammonium'salts or salts of alkali-metals other than potassium. I havefound that aqueous solutions of sodium, ammonium or lithum salts havethe property of bringing about the dissolution of the water-insolublepotassium metaphosphate in aqueous solutions. For example, I haveemployed sodium metaphosphate, sodium chloride, ammonium chloride,sodium carbonate and lithium chloride separately in aqueous solutionsfor bringing about the dissolution of the crystalline water-insolublepotassium metaphosphate. The sodium metaphosphate may be either theglassy sodium metaphosphate commonly known as sodium hexametaphosphate(NaPOahs or Grahams salt, or the water-soluble crystalline sodiummetaphosphate commonly known as sodium trimetaphosphate (N aPO3)3; I mayeven use as the dissolving agent for the crystalline potassiummetaphosphate the crystalline form of sodium metaphosphate commonlyknown as Maddrell salt, which is sometimes re ferred to as insolublesodium metaphosphate.

This Maddrell salt is much less soluble than the Grahams salt or sodiumtrimetaphosphate but nevertheless is sufiiciently soluble to cause theformation of a viscous solution of crystalline potassium metaphosphateafter a considerable time. A 10% aqueous solution of sodiumtrimetaphosphate in distilled water can readily be made.

The manner of making glassy sodium metaphosphate commonly known assodium hexametaphosphate or Graham's salt, the crystalline sodiumtrimetaphosphate and the so-called insoluble form of sodiummetaphosphate are fully disclosed in the paper by Partridge, Hicks andSmith entitled A thermal, microscopic, and X-ray study of the systemNaPO3-Na4P2O7, in the Journal of the American Chemical Society forFebruary 1941. Briefly, the glassy sodium metaphosphate may be made byheating to fusion mono'sodium dihydrogen orthophosphate and rapidlycooling the melt. The sodium trimetaphosphate may be made by heatingmonosodium dihydrogen orthophosphate to a temperature between 500 C. andits melting point of 625 C. or by slow cooling from above the meltingpoint. The insoluble form or forms of sodium metaphosphate may be madeby heating monosodium dihydrogen orthophosphate in the temperature rangebetween 300 P s ma rema e by mixin 0 ra mmune er t i n assium e etau iphate in '80 ml. water and adding thereto a solution' of 10 grams sodiummetaphosphate (Grahams salt) in 30 ml. of Water. It is of course to beunderstood that instead of adding a solution of sodium metaphosphate tothe water contain g potassium metaphosphate, the sodium metaphos; phatemay be mixed with the potassium rnetaphosphate and the mixture added tothe water but it is more diilicult to obtain a satisfactory product inthis manner for assoona s theothere The invention is not limited to theexamples given or the preferred methods, but may be otherwise embodiedor practiced within the scope of the following claims. 7

I claim:

" A it eous s t q sn'ems contai in a ceramic pigment and a viscousaqueous solution resulting from dissolving crystalline water -insolublepotassium metaphosphate in water cont i g water soluble inorganic saltof the class ing of ammonium salts and salts of an alkali-meta} otherthan potassium.

A. vitreous paint or enamel containing a cer mic igmentand a viscousaqueous solution m y P.. a

wise insoluble particles of potassium metaphose .phate come in contactwith the sodium salt-solution, they gelatinize on the surface and it isdifiicult to get them wholly into solution. [This is also the"'casewhere'other 'saltsare employed for causing the dissolution of themetaphosphate in water. A sol-ution of potassium meta-phosphate insodium metaphosphate is preferred since it is substantially more viscousthan a solution pf potassiummetaphospha-te in other sodium salts such assodium chloride.

Otherwater-insoluble metaphos-phates may be employed place of thecrystalline potassium meta-phosphate, Lead metaphosphate 53b (11 0s);

may "be ri ade by heating lead nitrate and phosphor-ic acid to atemperature of about 415 G. The "lead metaphosphatemay then be dissolvedin anaqueous solution of ammonium sulphide to form a viscousmetaphosphate paint vehicle. This viscous metaphosphate solution mixesWell with ceramic pigments, mas be easily applied to the article with abrush and-form a hard ads herent when bur-neg at a temperature of abou 8The viscous metaphosphate solution is capable of being used for otherpurposes than as a-vehicle for ceramic pigments. "it may be used as aseramie cement or bond for refractories and for other purposes whichinvolve heating the solution to a high temperature to form a hard adhereut resulting from dissolving crystalline water-insolublepotassiummetaphosphate in an aqueous solution of a water soluble inorganic sodiumsalt.

3, vitreous paint or enamel containing a ceramic pigment and a viscousaqueous solution resulting from dissolving crystalline water-insolublepotassium metaphosphate in an aqueous solution of sodium metaphosphate.l

4:. A ceramic paint vehicle adapted-and intended for use with ceramicpigments in the production of ceramic paints, said'vehicle comprising atroom temperature a viscous aqueous solution-resulting from dissolvingcrystalline waterinsoluble potassium metaphosphate in aqueous solutionof water soluble inorganic salt of the class'consisting of ammoniumsalts andsalts-oi an alkali-metal other than potassium.

- 5. A ceramic paint vehicle adapted and intended for use with ceramicpigments in the-production of ceramic paints, said vehicle-compgis ingat room temperature a viscous aqueous solution resulting fromdissolvingcrystalline waterinsoluble potassium metaphosphate-in anaquee oussolution of water soluble inorganic sodium salt.

6. A ceramic pain-t vehicle adapted and -intended for use with ceramicpigmentsin theproduction of ceramic paints, said vehicle comprise ing aviscous aqueous solution resultingfrom dissolving crystallinewater-insolub-le potassium metaphosphate in an aqueous sol-utionptodiummetaphosphate.

\ A. aacnson.

